Conventional packaged semiconductor devices have been produced by bonding a semiconductor element to a die pad of a lead frame with an adhesive such as a silver paste, connecting it with the lead frame by wire-bonding and then sealing the whole body except outer leads for external connection. However, with a recent demand for packaged semiconductor devices of higher density and smaller area and thickness, packages of various structures have been developed. Some examples are LOC (lead on chip) and COL (chip on lead), but are not decreased enough in area and thickness.
Another approach developed to solve these problems is a package structure wherein only one side of packages (the side bearing semiconductor elements) is sealed to use the exposed backside of lead frames for external connection. Packages of this structure achieve the decrease in area and thickness because lead frames do not protrude from sealing resin, but the sealing resin tends to creep even on the backside of lead frames.
The inventors have found that such a trouble might be prevented by protecting the backside of lead frames by bonding an adhesive film and peeling it off after sealing. This method needs an adhesive film which has enough bonding strength to lead frames and, after resin sealing, can be peeled off easily with heat or the like. However, there has been no adhesive film for semiconductor that possesses both the antipodal properties.